Scrubbing Spacer for Gas Storage Well

Abstract

In recent years, the utilization of underground gas storage wells in the Kingdom of Saudi Arabia (KSA) has witnessed significant growth. This strategic approach enables the operator to effectively reserve natural gas for the long term and optimize the management of supply-demand dynamics. In a natural gas storage well, the casing and the cement sheath surrounding it are critical barriers to withstand downhole stress cycles and ensure long term well integrity. Cement evaluation logs are performed, and the cement sheath quality is analyzed to decide whether the well can be completed for gas injection or remedial work is necessary. Hence, a proper cement design plays a vital role in the successful construction of such wells. A major aspect of any cement design is mud removal. Effective removal of drilling fluids is crucial to a successful cementing operation. However, drilling fluids are becoming more resilient, especially Non-Aqueous Fluids (NAF) with increasingly complex hydrocarbon chains and strong reverse-emulsions. Therefore, it is ever more difficult for conventional spacers to clean NAF-containing wellbores and water-wet casing surfaces, resulting in poor cement bonding and lack of zonal isolation. Conventionally, a surfactant is used to invert the emulsion and water-wet the surfaces, while a mutual solvent is added to disperse and dissolve the oil droplets. Since the formulations of NAF vary greatly, a universal spacer formulation suitable for all applications does not exist. To solve this problem, the spacer performance is augmented by introducing scrub fibers to promote mud removal. The fibers enhance flow shearing and attract non-aqueous compounds through hydrophobic-hydrophobic interaction. A rotor-cleaning test using a sandblasted rotor facilitates the evaluation the spacer cleaning performance in the laboratory and tune its formulation. Consequently, the enhanced spacer design has improved cement bonding to casing and wellbore across the critical well interval. The clear improvement seen on the cement evaluation logs has been well recognized. So far, a 100% success rate is maintained. An engineered scrubbing spacer which includes a fiber in the spacer to substantially improve NAF removal during cementing operations. It has also been shown to improve the removal of water-based drilling fluids that are sticky and difficult to clean.